To protect the environment, regulations are being enacted to ensure that leaks of hazardous materials from underground pipelines are detected in a timely way to limit spill sizes. One such procedure is the Environmental Protection Agency procedure, "EPA--Standard Test Procedures for Evaluating Leak Detection Methods: Pipeline Leak Detection Systems". This procedure requires that leaks as small as 3 gph at a 10-psi line pressure must be detected.
In some cases, the only practical method of leak detection is to pressurize the pipeline under static conditions (that is, with valves closed at each end, thereby preventing flow through the pipeline) and then monitor the line pressure for a suitable period to detect a leak. This approach may be referred to as the "pressure decay" method. Given the accurate pressure sensors available today, it is possible to detect leaks as small as 3 gph at 10 psi by monitoring the decay of pressure caused by the leak. The pressure decay method requires that the pipeline temperature be held constant or that changes in temperature over the length of the pipeline be accounted for. Temperature stability or compensation is required since a slight decrease in temperature can also cause pressure decay, a pressure decay which can be mistaken for a leak.
Because maintaining temperature stability is difficult in some situations, the pressure decay method is limited in its use. In many instances, the time required for temperature to equilibrate or stabilize is so long that it imposes unacceptably long downtimes on an operational pipeline. In others instances, sufficient temperature equilibrium may not be attainable.
Compensating for the effects of temperature on buried pipelines can also be too complex or expensive to be practical. Rarely has an array of suitable temperature sensors been installed at the time of pipeline construction.